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                <h2 id="JDBC"><a href="#JDBC" class="headerlink" title="JDBC"></a>JDBC</h2><ol>
<li>JDBC基本概念<br> Java DataBase Connectivity<br> Java数据库连接，Java语言操作数据库<br> JDBC本质：官方定义了一套操作所有关系型数据库的规则(接口),各个厂商去实现这套接口,提供数据库驱动jar包.<br>       我们可以使用这套接口编程,真正执行的代码时驱动jar包中的实现类<br><br> 期望使用统一的一套Java代码可以操作所有关系型数据库。<br> 每一个厂商写类自己数据库的JDBC实现类</li>
</ol>
<span id="more"></span>

<ol start="2">
<li>快速入门<br> 步骤:<br> 1. 导入驱动jar包<br>     1. 复制jar文件到项目的libs目录下<br>     2. 右键–&gt;add as Library<br><br> 2. 注册驱动<br> 3. 获取数据库连接对象 Connection<br> 4. 定义sql<br> 5. 获取执行sql语句的对象 Statement<br> 6. 执行sql,接受返回结果<br> 7. 处理结果<br> 8. 释放资源</li>
</ol>
<p>&#x2F;**</p>
<ul>
<li>JDBC快速入门<br> *&#x2F;<br>public class JdbcDemo1 {<br> public static void main(String[] args) throws Exception {<br> &#x2F;&#x2F;1. 导入驱动jar包 mysql-connector-java-8.0.19.jar<br> &#x2F;&#x2F;2. 注册驱动<br> Class.forName(“com.mysql.cj.jdbc.Driver”);<br> &#x2F;&#x2F;3. 获取数据库连接对象<br> Connection connection &#x3D; DriverManager.getConnection(“jdbc:mysql:&#x2F;&#x2F;localhost:3306&#x2F;lovelycc?serverTimezone&#x3D;UTC”, “root”, “root”);<br> &#x2F;&#x2F;4. 定义sql语句<br> String sql &#x3D; “update hero set weight &#x3D; 57 where id &#x3D; 1”;<br> &#x2F;&#x2F;5. 获取执行sql的对象 Statement<br> Statement statement &#x3D; connection.createStatement();<br> &#x2F;&#x2F;6. 执行sql<br> int count &#x3D; statement.executeUpdate(sql);<br> &#x2F;&#x2F;7. 处理结果<br> System.out.println(count);<br> &#x2F;&#x2F;8. 释放资源<br> statement.close();<br> connection.close();<br> }<br>}</li>
</ul>
<ol start="3">
<li><p>详解各个对象</p>
</li>
<li><p>DriverManager: 驱动管理对象<br> 功能:<br> 1. 注册驱动: 告诉程序该使用哪一个数据库驱动jar<br>     Class.forName(“com.mysql.cj.jdbc.Driver”);<br>     在com.mysql.cj.jdbc.Driver类中存在静态代码块注册驱动<br><br>     注意: mysql5之后的驱动jar包可以省略注册驱动的步骤<br><br> 2. 获取数据库连接<br>     方法: static Connection getConnection(String url, String user, String password)<br>     参数:<br>         url: 指定连接的路径<br>             语法: jdbc:mysql:&#x2F;&#x2F;ip地址(域名):端口号&#x2F;数据库名称<br>                   jdbc:mysql:&#x2F;&#x2F;localhost:3306&#x2F;lovelycc<br>                   如果连接本机,端口是默认的3306,可以省略成jdbc:mysql:&#x2F;&#x2F;&#x2F;lovelycc<br>         user:用户名 root<br>         password:密码 root
         </p>
</li>
<li><p>Connection: 数据库连接对象</p>
<ol>
<li>功能:<ol>
<li>获取执行sql的对象<br> Statement createStatement()<br> PreparedStatement prepareStatement(String sql)</li>
<li>管理事务:<br> 开启事务: setAutoCommit(boolean autoCommit): 调用该方法设置参数为false,即开启事务<br> 提交事务: commit()<br> 回滚事务: rollback()</li>
</ol>
</li>
</ol>
</li>
<li><p>Statement: 执行sql的对象<br> 用于执行静态SQL语句并返回其生成结果的对象</p>
<ol>
<li>执行sql<ol>
<li>boolean execute(String sql): 可以执行任意的sql (了解)</li>
<li>int executeUpdate(String sql): 执行DML(insert,update,delete)语句,DDL(create,alter,drop)语句<br> 返回值: 影响的行数,可以通过这个影响的行数判断DML语句是否执行成功,返回值&gt;0成功,反之失败</li>
<li>ResultSet executeQuery(String sql): 执行DQL(select)语句</li>
</ol>
</li>
<li>练习:<ol>
<li>hero表 添加一条记录</li>
</ol>
</li>
</ol>
</li>
</ol>
<hr>
<p>&#x2F;*<br>    hero表练习insert<br> *&#x2F;<br>public class JdbcDemo2 {<br>    public static void main(String[] args) {<br>        Connection connection &#x3D; null;<br>        Statement statement &#x3D; null;<br>        &#x2F;&#x2F;1. 注册驱动<br>        try {<br>            Class.forName(“com.mysql.cj.jdbc.Driver”);<br>            &#x2F;&#x2F;2. 定义sql<br>            String sql &#x3D; “insert into hero values(0,’楚留香’,18,60,188)”;<br>            &#x2F;&#x2F;3. 获取Connection对象<br>            connection &#x3D; DriverManager.getConnection(“jdbc:mysql:&#x2F;&#x2F;localhost:3306&#x2F;lovelycc?serverTimezone&#x3D;GMT%2B8&amp;useUnicode&#x3D;true&amp;characterEncoding&#x3D;utf8”, “root”, “root”);<br>            &#x2F;&#x2F;4. 获取执行sql的Statement对象<br>            statement &#x3D; connection.createStatement();<br>            &#x2F;&#x2F;5. 执行sql<br>            int count &#x3D; statement.executeUpdate(sql);<br>            &#x2F;&#x2F;6. 处理结果,影响的行数<br>            if(count&gt;0){<br>                System.out.println(“添加成功”);<br>            }else{<br>                System.out.println(“添加失败”);<br>            }<br>        } catch (ClassNotFoundException e) {<br>            e.printStackTrace();<br>        } catch (SQLException e) {<br>            e.printStackTrace();<br>        }finally{<br>            &#x2F;&#x2F;7. 释放资源<br>            &#x2F;&#x2F;避免空指针异常<br>            if(statement !&#x3D; null){<br>                try {<br>                    statement.close();<br>                } catch (SQLException e) {<br>                    e.printStackTrace();<br>                }<br>            }</p>
<pre><code>        if(connection != null)&#123;
            try &#123;
                connection.close();
            &#125; catch (SQLException e) &#123;
                e.printStackTrace();
            &#125;
        &#125;

    &#125;
&#125;
</code></pre>
<p>}</p>
<hr>
<pre><code>    2. hero表 修改记录
    
</code></pre>
<p>String sql &#x3D; “update hero set name &#x3D; ‘陆小凤’ where id &#x3D; 9”;</p>
<pre><code>    3. hero表 删除一条记录
</code></pre>
<p>String sql &#x3D; “update hero set name &#x3D; ‘delete from hero where name &#x3D; ‘ww’”;</p>
<pre><code>    4. DDL(create,alter,drop)语句
</code></pre>
<p>String sql &#x3D; “create table student (id int , name varchar(20))”;<br>…<br>&#x2F;&#x2F;处理结果 DDL语句statement.executeUpdate返回值一直为0<br>sout(count)</p>
<pre><code>    tips: 1. The server time... 时区问题: url后面加上serverTimezone=GMT%2B8
          2. 中文写进mysql变成???: url后面加上 useUnicode=true&amp;characterEncoding=utf8
          最终写成: &quot;jdbc:mysql://localhost:3306/lovelycc?serverTimezone=GMT%2B8&amp;useUnicode=true&amp;characterEncoding=utf8&quot;
          
          
          
</code></pre>
<ol start="4">
<li>ResultSet: 结果集对象, 封装查询结果<br> boolean next(): 游标向下移动一行,判断当前行是否有数据,有数据为true<br> getXxx(): 获取Xxx类型的数据<br> 参数: int: 代表列的编号,从1开始 如: getString(1)<br>       String: 代表列名称 如getDouble(“weight”)<br><br> 使用步骤:<ol>
<li>游标向下移动一行</li>
<li>判断是否有数据</li>
<li>获取数据</li>
</ol>
</li>
</ol>
<hr>
<p>public class JdbcDemo3 {<br>    public static void main(String[] args) {<br>        Connection connection &#x3D; null;<br>        Statement statement &#x3D; null;<br>        ResultSet resultSet &#x3D; null;<br>        &#x2F;&#x2F;1. 注册驱动<br>        try {<br>            Class.forName(“com.mysql.cj.jdbc.Driver”);<br>            &#x2F;&#x2F;2. 定义sql<br>            String sql &#x3D; “select * from hero “;<br>            &#x2F;&#x2F;3. 获取Connection对象<br>            connection &#x3D; DriverManager.getConnection(“jdbc:mysql:&#x2F;&#x2F;localhost:3306&#x2F;lovelycc?serverTimezone&#x3D;GMT%2B8&amp;useUnicode&#x3D;true&amp;characterEncoding&#x3D;utf8”, “root”, “root”);<br>            &#x2F;&#x2F;4. 获取执行sql的Statement对象<br>            statement &#x3D; connection.createStatement();<br>            &#x2F;&#x2F;5. 执行sql<br>            resultSet &#x3D; statement.executeQuery(sql);<br>            &#x2F;&#x2F;6. 处理结果,影响的行数<br>&#x2F;&#x2F;			&#x2F;&#x2F;6.1 游标向下移动一行<br>&#x2F;&#x2F;			resultSet.next();<br>            &#x2F;&#x2F;6.2 获取数据</p>
<pre><code>        //while循环判断
        while(resultSet.next())&#123;
            int id = resultSet.getInt(1);
            String name = resultSet.getString(&quot;name&quot;);
            double weight = resultSet.getDouble(&quot;weight&quot;);
            System.out.println(id+&quot;号选手&quot;+name+&quot;重达&quot;+weight+&quot;KG&quot;);
        &#125;

    &#125; catch (ClassNotFoundException e) &#123;
        e.printStackTrace();
    &#125; catch (SQLException e) &#123;
        e.printStackTrace();
    &#125;finally&#123;
        //7. 释放资源
        //避免空指针异常
        if (resultSet != null) &#123;
            try &#123;
                resultSet.close();
            &#125; catch (SQLException e) &#123;
                e.printStackTrace();
            &#125;
        &#125;

        if(statement != null)&#123;
            try &#123;
                statement.close();
            &#125; catch (SQLException e) &#123;
                e.printStackTrace();
            &#125;
        &#125;

        if(connection != null)&#123;
            try &#123;
                connection.close();
            &#125; catch (SQLException e) &#123;
                e.printStackTrace();
            &#125;
        &#125;
    &#125;
&#125;
</code></pre>
<h2 id=""><a href="#" class="headerlink" title="}"></a>}</h2><pre><code>练习:
定义一个方法,查询hero表的数据将其封装为对象,然后装载集合,返回,打印
1. 定义Hero类
2. 定义方法 public List&lt;Hero&gt; findAll()&#123;&#125;
3. 实现方法 select * from hero;
</code></pre>
<h2 id="x2F-封装Hero表数据的JavaBean-x2F"><a href="#x2F-封装Hero表数据的JavaBean-x2F" class="headerlink" title="&#x2F;*    封装Hero表数据的JavaBean *&#x2F;
 "></a>&#x2F;*<br>    封装Hero表数据的JavaBean<br> *&#x2F;
 </h2><p>public class Hero {<br>    &#x2F;&#x2F;定义成封装类比较好,可以接受null<br>    private Integer id;<br>    private String name;<br>    private Integer age;<br>    private Double weight;<br>    private Double height;</p>
<pre><code>@Override
public String toString() &#123;
    return &quot;Hero&#123;&quot; +
        &quot;id=&quot; + id +
        &quot;, name=&#39;&quot; + name + &#39;\&#39;&#39; +
        &quot;, age=&quot; + age +
        &quot;, weight=&quot; + weight +
        &quot;, height=&quot; + height +
        &#39;&#125;&#39;;
&#125;

public int getId() &#123;
    return id;
&#125;

public void setId(int id) &#123;
    this.id = id;
&#125;

public String getName() &#123;
    return name;
&#125;

public void setName(String name) &#123;
    this.name = name;
&#125;

public int getAge() &#123;
    return age;
&#125;

public void setAge(int age) &#123;
    this.age = age;
&#125;

public double getWeight() &#123;
    return weight;
&#125;

public void setWeight(double weight) &#123;
    this.weight = weight;
&#125;

public double getHeight() &#123;
    return height;
&#125;

public void setHeight(double height) &#123;
    this.height = height;
&#125;
</code></pre>
<p>}</p>
<hr>
<p>&#x2F;*<br>    定义一个方法,查询hero表的数据将其封装<br> *&#x2F;<br>public class JdbcDemo4 {<br>    public static void main(String[] args) {<br>        List<Hero> list &#x3D; new JdbcDemo4().findAll();<br>        System.out.println(list);<br>        System.out.println(list.size());</p>
<pre><code>&#125;

/*
    查询所有H象
 */
public List&lt;Hero&gt; findAll()&#123;
    Connection connection = null;
    Statement statement = null;
    ResultSet resultSet = null;
    List&lt;Hero&gt; list = null;

    //1. 注册驱动
    try &#123;
        Class.forName(&quot;com.mysql.cj.jdbc.Driver&quot;);
        //2. 定义sql
        String sql = &quot;select * from hero &quot;;
        //3. 获取Connection对象
        connection = DriverManager.getConnection(&quot;jdbc:mysql://localhost:3306/lovelycc?serverTimezone=GMT%2B8&amp;useUnicode=true&amp;characterEncoding=utf8&quot;, &quot;root&quot;, &quot;root&quot;);
        //4. 获取执行sql的Statement对象
        statement = connection.createStatement();
        //5. 执行sql
        resultSet = statement.executeQuery(sql);
        //6. 遍历结果集,封装对象,装载集合
        list = new ArrayList&lt;Hero&gt;();

        //while循环判断
        while(resultSet.next())&#123;
            int id = resultSet.getInt(&quot;ID&quot;);
            String name = resultSet.getString(&quot;name&quot;);
            int age = resultSet.getInt(&quot;age&quot;);
            double weight = resultSet.getDouble(&quot;weight&quot;);
            double height = resultSet.getDouble(&quot;height&quot;);
            //创建Hero对象,并赋值
            Hero hero = new Hero();
            hero.setId(id);
            hero.setName(name);
            hero.setAge(age);
            hero.setWeight(weight);
            hero.setHeight(height);

            //装载集合
            list.add(hero);
        &#125;

    &#125; catch (ClassNotFoundException e) &#123;
        e.printStackTrace();
    &#125; catch (SQLException e) &#123;
        e.printStackTrace();
    &#125;finally&#123;
        //7. 释放资源
        //避免空指针异常
        if (resultSet != null) &#123;
            try &#123;
                resultSet.close();
            &#125; catch (SQLException e) &#123;
                e.printStackTrace();
            &#125;
        &#125;

        if(statement != null)&#123;
            try &#123;
                statement.close();
            &#125; catch (SQLException e) &#123;
                e.printStackTrace();
            &#125;
        &#125;

        if(connection != null)&#123;
            try &#123;
                connection.close();
            &#125; catch (SQLException e) &#123;
                e.printStackTrace();
            &#125;
        &#125;
    &#125;
    return list;
&#125;
</code></pre>
<h2 id="-1"><a href="#-1" class="headerlink" title="}"></a>}</h2><p>代码重复度太高<br>抽取JDBC工具类: JDBCUtils<br>目的: 简化书写<br>分析:<br>    1. 抽取注册驱动<br>    2. 抽取一个方法获取连接对象<br>        需求：不想传递参数，太麻烦，还得保证工具类的通用性<br>        解决：配置文件<br>            jdbc.properties<br>                url&#x3D;<br>                user&#x3D;<br>                password&#x3D;<br>    3. 抽取一个方法释放资源</p>
<p>&#x2F;*<br>    JDBC工具类<br> *&#x2F;<br>public class JDBCUtils {<br>    private static String url;<br>    private static String user;<br>    private  static String password;<br>    private static  String driver;</p>
<pre><code>/*
    配置文件的读取,只需要读取一次即可拿到这些值.使用静态代码块
 */
static&#123;
    try &#123;
        //读取资源文件,获取值.
        //1. 创建Properties集合类
        Properties pro = new Properties();

        //获取src路径下的文件的方式 ---&gt; ClassLoader 类加载器
        //如果路径中存在空格，则会报系统找不到路径错误
        ClassLoader classLoader = JDBCUtils.class.getClassLoader();
        URL res = classLoader.getResource(&quot;jdbc.properties&quot;);
        String path = res.toURI.getPath();//URL对象转换成字符串前，先调用toURI()方法

        //2. 加载文件
</code></pre>
<p>&#x2F;&#x2F;			pro.load(new FileReader(“D:\IntelliJ IDEA Community Edition 2019.3.1\JDBCNote\jdbc\src\jdbc.properties”));<br>                pro.load(new FileReader(path));<br>            &#x2F;&#x2F;3. 获取数据<br>            url &#x3D; pro.getProperty(“url”);<br>            user &#x3D; pro.getProperty(“user”);<br>            password &#x3D; pro.getProperty(“password”);<br>            driver &#x3D; pro.getProperty(“driver”);<br>            &#x2F;&#x2F;注册驱动<br>            Class.forName(driver);<br>        } catch (IOException e) {<br>            e.printStackTrace();<br>        } catch (ClassNotFoundException e) {<br>            e.printStackTrace();<br>        } catch (URISyntaxException e) {<br>            e.printStackTrace();<br>        }<br>    }</p>
<pre><code>/*
    获取连接
    返回连接对象
 */

public static Connection getConnection() throws SQLException &#123;
    return DriverManager.getConnection(url,user,password);
&#125;


public static void close(Statement stmt, Connection conn)&#123;
        if(stmt != null)&#123;
            try &#123;
                stmt.close();
            &#125; catch (SQLException e) &#123;
                e.printStackTrace();
            &#125;
        &#125;
        if(conn != null)&#123;
            try &#123;
                conn.close();
            &#125; catch (SQLException e) &#123;
                e.printStackTrace();
            &#125;
        &#125;
&#125;
//重载方法
public static void close(ResultSet res,Statement stmt, Connection conn)&#123;
    if(res != null)&#123;
        try &#123;
            res.close();
        &#125; catch (SQLException e) &#123;
            e.printStackTrace();
        &#125;
    &#125;
    if(stmt != null)&#123;
        try &#123;
            stmt.close();
        &#125; catch (SQLException e) &#123;
            e.printStackTrace();
        &#125;
    &#125;
    if(conn != null)&#123;
        try &#123;
            conn.close();
        &#125; catch (SQLException e) &#123;
            e.printStackTrace();
        &#125;
    &#125;
&#125;
</code></pre>
<h2 id="-2"><a href="#-2" class="headerlink" title="}"></a>}</h2><p>public List<Hero> findAll2(){<br>        Connection connection &#x3D; null;<br>        Statement statement &#x3D; null;<br>        ResultSet resultSet &#x3D; null;<br>        List<Hero> list &#x3D; null;</p>
<pre><code>    //1. 注册驱动
    try &#123;
        //1. 获取Connection对象
        connection = JDBCUtils.getConnection();
        //2. 定义sql
        String sql = &quot;select * from hero &quot;;
        //4. 获取执行sql的Statement对象
        statement = connection.createStatement();
        //5. 执行sql
        resultSet = statement.executeQuery(sql);
        //6. 遍历结果集,封装对象,装载集合
        list = new ArrayList&lt;Hero&gt;();

        //while循环判断
        while(resultSet.next())&#123;
            int id = resultSet.getInt(&quot;ID&quot;);
            String name = resultSet.getString(&quot;name&quot;);
            int age = resultSet.getInt(&quot;age&quot;);
            double weight = resultSet.getDouble(&quot;weight&quot;);
            double height = resultSet.getDouble(&quot;height&quot;);
            //创建Hero对象,并赋值
            Hero hero = new Hero();
            hero.setId(id);
            hero.setName(name);
            hero.setAge(age);
            hero.setWeight(weight);
            hero.setHeight(height);

            //装载集合
            list.add(hero);
        &#125;
    &#125; catch (SQLException e) &#123;
        e.printStackTrace();
    &#125;finally&#123;
        //7. 释放资源
        //避免空指针异常
        JDBCUtils.close(resultSet,statement,connection);
    &#125;
    return list;
&#125;
</code></pre>
<p>练习:<br>    需求:<br>        1. 通过键盘录入用户名和密码<br>        2. 判断用户是否登录成功<br>            SELECT * FROM USER WHERE username &#x3D; “” and password &#x3D; “”;<br>            如果sql有查询结果,则成功,反之失败<br>    步骤:<br>        1. 创建数据库表 user表<br>CREATE TABLE USER(<br>    id INT PRIMARY KEY AUTO_INCREMENT,<br>    username VARCHAR(32),<br>    PASSWORD VARCHAR(32)<br>);<br>SELECT * FROM USER;<br>INSERT INTO USER VALUES(0,’西门吹雪’,’123’);<br>INSERT INTO USER VALUES(0,’陆小凤’,’456’);<br>SELECT * FROM USER;</p>
<pre><code>    2. 创建登录方法
</code></pre>
<p>public class JDBCDemo5 {<br>    public static void main(String[] args) {<br>        &#x2F;&#x2F;1. 键盘录入<br>        Scanner sc &#x3D; new Scanner(System.in);<br>        System.out.println(“请输入用户名:”);<br>        String username &#x3D; sc.nextLine();<br>        System.out.println(“请输入密码:”);<br>        String password &#x3D; sc.nextLine();</p>
<pre><code>    boolean flag = new JDBCDemo5().login(username, password);
    if (flag)&#123;
        System.out.println(&quot;登录成功&quot;);
    &#125;else&#123;
        System.out.println(&quot;登陆失败&quot;);
    &#125;

    //2. 调用方法

    //3. 判断结果,输出不同语句
&#125;

/*
    登录方法
 */
public boolean login(String username,String password)&#123;
    Connection connection = null;
    Statement statement = null;
    ResultSet resultSet = null;
    if (username == null || password == null)&#123;
        return false;
    &#125;
    //连接数据库判断是否登陆成功
    try &#123;
        connection = JDBCUtils.getConnection();
        //定义sql
        String sql = &quot;select * from user where username = &#39;&quot;+username+&quot;&#39; and password = &#39;&quot;+password+&quot;&#39;&quot;;
        statement = connection.createStatement();
        resultSet = statement.executeQuery(sql);
        //判断是否有数据,有则登陆成功
        return resultSet.next();
    &#125; catch (SQLException e) &#123;
        e.printStackTrace();
    &#125;finally&#123;
        JDBCUtils.close(resultSet,statement,connection);
    &#125;
    return false;
&#125;
</code></pre>
<h2 id="-3"><a href="#-3" class="headerlink" title="}"></a>}</h2><ol start="5">
<li>PreparedStatement: 执行sql的对象<ol>
<li>SQL注入问题: 在拼接sql时,有一些sql的特殊关键字参与字符串拼接,会造成安全性问题<ol>
<li>输入用户名随便,输入密码: a’ or ‘a’ &#x3D; ‘a<br> select * from user where username &#x3D; ‘sssss’ and password &#x3D; ‘a’ or ‘a’ &#x3D; ‘a’<br> 最后恒为true,从而登陆成功</li>
</ol>
</li>
<li>解决sql注入问题: 使用PreparedStatement对象来解决</li>
<li>预编译的SQL: 参数使用?作为占位符</li>
<li>步骤:<ol>
<li><p>导入驱动jar包</p>
</li>
<li><p>注册驱动</p>
</li>
<li><p>获取数据库连接对象 Connection</p>
</li>
<li><p>定义sql<br> 注意: sql的参数使用?作为占位符,如 select * from user where username &#x3D; ? and password &#x3D; ?;</p>
</li>
<li><p>获取执行sql语句的对象 PreparedStatement Connection.prepareStatement(String sql)</p>
</li>
<li><p>给?赋值<br> 方法: setXxx(参数1,参数2);<br> 参数1: ?的位置<br> 参数2: ?的值</p>
</li>
<li><p>执行sql,接受返回结果,不需要再传递sql语句</p>
</li>
<li><p>处理结果</p>
</li>
<li><p>释放资源<br> public boolean login(String username,String password){<br> Connection connection &#x3D; null;<br> PreparedStatement preparedstatement &#x3D; null;<br> ResultSet resultSet &#x3D; null;<br> if (username &#x3D;&#x3D; null || password &#x3D;&#x3D; null){<br> return false;<br> }<br> &#x2F;&#x2F;连接数据库判断是否登陆成功<br> try {<br> connection &#x3D; JDBCUtils.getConnection();<br> &#x2F;&#x2F;定义sql<br>&#x2F;&#x2F;			String sql &#x3D; “select * from user where username &#x3D; ‘“+username+”‘ and password &#x3D; ‘“+password+”‘“;<br> String sql &#x3D; “select * from user where username &#x3D; ? and password &#x3D; ?”;</p>
<p> preparedstatement &#x3D; connection.prepareStatement(sql);<br> &#x2F;&#x2F;给问号赋值<br> preparedstatement.setString(1,username);<br> preparedstatement.setString(2,password);<br> &#x2F;&#x2F;不需要再传递sql了<br> resultSet &#x3D; preparedstatement.executeQuery();<br> &#x2F;&#x2F;判断是否有数据,有则登陆成功<br> return resultSet.next();</p>
</li>
</ol>
<p> } catch (SQLException e) {<br>     e.printStackTrace();<br> }finally{<br>     JDBCUtils.close(resultSet,preparedstatement,connection);<br> }<br> return false;</p>
</li>
</ol>
<p> }</p>
</li>
</ol>
<hr>
<p>注意: 后期都会使用PreparedStatement对象来完成增删改查的操作<br>    1. 可以防止SQL注入<br>    2. 效率更高</p>
<h2 id="JDBC控制事务"><a href="#JDBC控制事务" class="headerlink" title="JDBC控制事务"></a>JDBC控制事务</h2><pre><code>1. 事务: 一个包含多个步骤的业务操作.如果这个业务操作被事务管理,则这多个步骤要么同时成功,要么同时失败.
2. 操作:
    开启事务: setAutoCommit(boolean autoCommit): 调用该方法设置参数为false,即开启事务
        在执行sql之前开启事务
    提交事务: commit()
        当所有sql都执行完提交事务
    回滚事务: rollback()
        在catch中回滚事务
3. 使用Connection对象来管理事务
</code></pre>
<p>银行转账案例:</p>
<p>CREATE TABLE account(<br>    id INT PRIMARY KEY AUTO_INCREMENT,<br>    NAME VARCHAR(32),<br>    balance DOUBLE<br>);<br>INSERT INTO account VALUES(0,’西门吹雪’,2000.55);<br>INSERT INTO account VALUES(0,’陆小凤’,3000.77);<br>SELECT * FROM account;</p>
<hr>
<p>&#x2F;*<br>    事务操作<br> *&#x2F;<br>public class JDBCDemo6 {<br>    public static void main(String[] args) {<br>        Connection connection &#x3D; null;<br>        PreparedStatement preparedStatement1 &#x3D; null;<br>        PreparedStatement preparedStatement2 &#x3D; null;<br>        try {<br>            connection &#x3D; JDBCUtils.getConnection();</p>
<pre><code>        //开启事务, 中间出现异常则停止转账,不然钱就不翼而飞了
        connection.setAutoCommit(false);

        //陆小凤-500,西门吹雪+500
        String sql1 = &quot;update account set balance = balance-? where name = ?&quot;;
        String sql2 = &quot;update account set balance = balance+? where name = ?&quot;;

        preparedStatement1 = connection.prepareStatement(sql1);
        preparedStatement2 = connection.prepareStatement(sql2);
        preparedStatement1.setDouble(1,300);
        preparedStatement1.setString(2,&quot;陆小凤&quot;);
        preparedStatement2.setDouble(1,300);
        preparedStatement2.setString(2,&quot;西门吹雪&quot;);
        preparedStatement1.executeUpdate();

        //手动制造异常
        int x = 3/0;
        preparedStatement2.executeUpdate();

        //提交事务
        connection.commit();
        //改成Exception,不管出现什么异常都进入回滚,回到事务开启之前的状态
    &#125; catch (Exception e) &#123;
        //事务回滚
        try &#123;
            if(connection!=null)&#123;
                connection.rollback();
            &#125;

        &#125; catch (SQLException ex) &#123;
            ex.printStackTrace();
        &#125;
        e.printStackTrace();
    &#125;finally &#123;
        JDBCUtils.close(preparedStatement1,connection);
        JDBCUtils.close(preparedStatement2,null);
    &#125;
&#125;
</code></pre>
<h2 id="-4"><a href="#-4" class="headerlink" title="}"></a>}</h2>
                
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